RF measurement feedback control and diagnostics for a plasma immersion ion implantation reactor

Abstract

A method of measuring ion dose in a plasma immersion ion implantation reactor during ion implantation of a selected species into a workpiece includes placing the workpiece on a pedestal in the reactor and feeding into the reactor a process gas comprising a species to be implanted into the workpiece, and then coupling RF plasma source power to a plasma in the reactor. It further includes coupling RF bias power to the workpiece by an RF bias power generator that is coupled to the workpiece through a bias feedpoint of the reactor and measuring RF current at the feedpoint to generate a current-related value, and then integrating the current-related over time to produce an ion implantation dose-related value.

Description

BACKGROUND OF THE INVENTION[0001]Ion implantation processes in integrated circuit fabrication typically require instrumentation and control to achieve a desired ion dose on a semiconductor wafer. The dose is the total number of ions per unit area passing through an imaginary surface plane of the wafer. The implanted ions distribute themselves throughout the volume of the wafer. The principal variation in implanted ion density (number of ions per unit volume) occurs along the direction of the ion flux, usually the perpendicular (vertical) direction relative to the wafer surface. The distribution of ion density (ions per unit volume) along the vertical direction is referred to as the ion implantation depth profile. Instrumentation and control systems for regulating ion implant dose (ions per unit area) is sometimes referred to as dosimetry.[0002]Ion beam implant machines, which generate a narrow ion beam that must be raster-scanned over the surface of the wafer, typically implant only...

AI Technical Summary

Benefits of technology

The patent describes methods for measuring the ion dose and energy during plasma immersion ion implantation. The methods involve measuring the current and voltage in the plasma, and using an ion efficiency factor to determine the proportion of the selected species relative to the total ions implanted. The methods can be used in a feedback control loop to adjust the power level and ensure accurate dosage control. The patent also describes a method for measuring the power-related value of the plasma, which can be used to adjust the RF plasma source power. Overall, the methods provide accurate and efficient means for measuring the ion dose and energy during plasma immersion ion implantation.

Problems solved by technology

This is critical in an ion beam implant machine, because it employs a D.C. ion source, which is subject to significant drift in its output current, and the various grids and electrodes employed in the beam implant machine drift as well (due to the susceptibility of a D.C. source to accumulation of deposited material on component surfaces).

In contrast, plasma immersion ion implantation reactors present a difficult problem in dosimetry.

Typically, the atomic weight of the ions incident on the wafer cannot be precisely determined because such a reactor employs a precursor gas containing the desired ion implantation species as well as other species.

As a result, determining the boron dose from a measured current is difficult.

Another difficulty in implementing dosimetry in a plasma immersion ion implantation reactor is that the plasma ions impact the entire wafer continuously, so that it is difficult to effect a direct measurement above the wafer of the total ion current to the wafer.

A further difficulty encountered in some plasma immersion ion implantation reactors is the presence of electromagnetic noise or interference in the chamber that can prevent a precise measurement of ion current.

Plasma immersion ion implantation reactors employing D.C. (or pulsed D.C.) plasma source power are susceptible to drift in the plasma ion current due to deposition of material on internal reactor components from the plasma.

One problem with such an arrangement is that the current measurement cannot distinguish between different atomic species, and therefore cannot provide an accurate measurement of the species of interest (e.g., boron).

Another problem is that the transmission of the measured current from the current sensor inside the cathode interior to an external controller or processor can be distorted by the noisy electromagnetic environment of the plasma reactor.

Another problem is that the orifice in the cathode constitutes an intrusion upon the ideal plasma environment, because the orifice can distort the electric field in the vicinity of the wafer periphery.

Furthermore, plasma passing through the orifice can cause problems by either sputtering the orifice surfaces or by depositing on the orifice interior surfaces, requiring the periodic cleaning of the orifice interior.

Moreover, real-time dose measurement in such a reactor is difficult.

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